[ATAC-Helicopter]

Summary

• Start the Avalonia mixer against the existing reconnecting PipeWire backend and persistent identity resolver.
• Dispatch immutable mixer snapshots onto the UI thread and show stable application rows with volume, mixed-volume state, and mute controls.
• Disable controls on disconnect; keep raw node and process identifiers out of normal UI.
• Add view-model tests and a screenshot captured from an isolated, silent PipeWire fixture.

Closes #38.

Screenshot

Verification and limits

• FADRIO_RUN_PIPEWIRE_INTEGRATION=1 ./scripts/test.sh passed locally, including managed/native tests and isolated PipeWire integration.
• dotnet format Fadrio.slnx --verify-no-changes --no-restore, roadmap audit, and diff checks passed.
• Launched the actual Avalonia window and captured the row from a controlled PipeWire fixture. On-screen slider dragging and screen-reader output are not yet independently qualified.
• Volume slider and mute button are keyboard-capable Avalonia controls with per-application automation names. Output control, icons, tray, and polish remain separate roadmap items.
• No packaging change. GitHub Actions will be canceled because Actions minutes are exhausted; remote CI is not claimed.